1. Field of the Invention
The present invention relates to a composition of a getter, and more particularly, to a composition of a getter and a field emission display using the same that is capable of lowering a temperature of an activation.
2. Description of the Background Art
In general, recently, various flat panel displays are being developed to reduce a weight and a volume, the shortcomings of a cathode ray tube (CRT).
The flat panel displays include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel, an electro-luminescence (EL), and the like. In order to improve a display quality, researches are being actively conducted to heighten a luminance, a contrast and a colorimetric purity of the flat panel display.
The FED is classified into a tip type FED in which a high electric field is concentrated on an acuminate emitter to emit electrons by a quantum mechanical tunnel effect, and a metal insulator metal (MIM) FED in which a high electric field is concentrated on a metal having a certain area to emit electrons by the quantum mechanical tunnel effect.
FIG. 1 is a perspective view of a tip type field emission display in accordance with a conventional art, and FIG. 2 is a sectional view of the tip type FED in accordance with the conventional art.
As shown in FIGS. 1 and 2, the FED includes an upper glass substrate 2 on which an anode electrode 4 and a fluorescent material 6 are stacked; and a field emission array 32 formed on the lower glass substrate 8.
The field emission array 32 includes a cathode electrode 10 and a resistance layer 12 sequentially formed on the lower substrate 8, a gate insulation layer 14 and an emitter 22 formed on the resistance layer 12, and a gate electrode 16 formed on the gate insulation layer 14.
The cathode electrode 10 supplies current to the emitter 22, and the resistance layer 12 restricts an overcurrent applied to the emitter 2 from the cathode electrode 10 in order to supply a uniform current to the emitter 22.
The gate insulation layer 14 insulates the cathode electrode 10 and the gate electrode 16.
The gate electrode 16 is used as a fetch electrode for fetching electrons.
A spacer 40 is installed between the upper glass substrate 2 and the lower glass substrate 8.
The spacer 40 supports the upper glass substrate 2 and the lower glass substrate 8 so that a high vacuum state can be maintained between the upper glass substrate 2 and the lower glass substrate 8.
For example, in order to display a picture, a negative polarity (xe2x88x92) cathode voltage is applied to the cathode electrode 10 and a positive polarity (+) anode voltage is applied to the anode electrode 4. And, a positive polarity (+) gate voltage is applied to the gate electrode 16.
Thereafter, electron beams 30 emitted from the emitter 22 collide with the fluorescent material 6 of red, green blue colors to excite the fluorescent material (phosphor). At this time, a visible ray of one of red, green and blue colors is luminescent. In this respect, in order to control each pixel, the FED is formed with a matrix structure as shown by the portion xe2x80x98Axe2x80x99 of FIG. 1.
FIG. 3 is a perspective view showing a gate structure of the FED in accordance with the conventional art, that is, a perspective view showing a gate structure formed in the matrix structure.
First, the cathode electrode 10 and the gate electrode 16 are electrically insulated by the gate insulation layer 14 and formed to cross each other in a horizontal or in a vertical direction.
Gate holes 36 are formed at the gate electrode 16 and emitters 22 corresponding to each gate hole 36 are formed on the cathode electrode 10.
Thereafter, when the cathode electrode 10 is grounded and some +100V voltage is applied to the gate electrode 16, a high electric field is generated at the end portions of the emitters 22 positioned at the part where the two electrodes 10 and 16 cross each other, and electrons 30 are emitted by the high electric field.
At this time, the voltage of the gate electrode 16 is lowered down as the size of the gate hole 36 is reduced, and the voltage of the gate electrode 16 differs depending on the characteristics of the material of the emitter 22. And, by applying a voltage sequentially to the cathode electrodes 10 and the gate electrodes 16, electrons 30 are emitted from the emitter 22 at the point where the two electrodes 10 and 16 cross each other so that the fluorescent material 6 is excited and accordingly light can be emitted from the pixels.
For example, a high pressure of above a few kV is applied to the anode electrode 4 coated with the fluorescent 6 thereon, in order to accelerate the electrons 30 emitted from the emitter 22 so that the electrons are collide with the fluorescent material 6.
At this time, as for the luminance of each pixel and color implementation, the luminance of the pixel can be controlled by using a principle that the amount of current differs according to a voltage difference applied between the emitter 22 and the gate electrode 16 and the color can be implemented by controlling the luminance of the three pixels of adjacent red, green and blue.
The electric field emission space inside the panel of the FED should be maintained in a high vacuum state of above 10xe2x88x925 Torr in view of its driving characteristics.
That is, the emitter 22 and the gate electrode 16 are separated with a space of about a sub-micron therebetween, into which a high electric field of about 107 V/cm is applied.
At this time, unless the space between the emitter 22 and the gate electrode 16 is maintained in the high vacuum state, the voltage between the emitter 22 and the gate electrode 16 may be emitted or an insulator destruction phenomenon may occur.
In addition, unless the electric field emission space is maintained in the high vacuum state, neutral particles existing inside the panel collide with the electrons to generate positive ions.
The generated positive ions collide with the emitter 22 to degrade the emitter 22 or collide with the electrons 30 to reduce an acceleration energy of the electrons 30 to degrade the luminance.
Thus, in order to improve the luminance, a vacuum process is necessary to make inside the panel to be in a high vacuum state during the fabrication process of the FED.
FIG. 4 is a sectional view showing a panel structure of the FED in accordance with the conventional art. That is, FIG. 4 is to show the getter. Descriptions for constructions repeatedly shown in FIGS. 1 and 3 are omitted.
As shown in FIG. 4, the panel of the FED includes an upper glass substrate 2 on which the anode electrode 4 and the fluorescent material 6 are stacked; a cathode electrode 10 and an insulation layer 14; a gate electrode 16 formed on the insulation layer 14; a lower glass substrate 8 with a focussing insulation layer (not shown) formed on the gate electrode 16; and a glass frit seal 38 supporting the upper glass substrate 2 and the lower glass substrate 8.
In addition, a getter 34 is formed inside the panel to absorb a gas generated during the FED fabrication process before the upper glass substrate 2 and the lower glass substrate 8 are attached.
The getter 34 is classified into an evaporable getter (EG) and a non-evaporable getter (NEG).
Barium is used as a material of the EG, and the EG is used for a cathode-ray tube forming a television screen and a computer screen. That is, the barium getter is evaporated by an external heating from an inner wall of the cathode-ray tube and used to remove a residual gas inside the cathode-ray tube as a metal film form.
In this respect, barium exists as a precursor of BaAl4+Ni before activation, and the activation process is performed when the precursor of barium is evaporated by the external heating.
Substantially, a mixture of powder of the composition BaAl4 and power of nickel is used as the precursor of the barium film.
Nickel is reacted with aluminum at a temperature of about 850xc2x0 C. and the heat generated by the reaction evaporates barium according to a xe2x80x98freshxe2x80x99 phenomenon.
However, the conventional art has problems that the structure for forming the EG inside the panel of the FET is complicated and when the EG is activated, the internal temperature goes up to 800xcx9c1250xc2x0 C. Thus, in case of the thin film display such as the FED, it is difficult to maintain the degree of vacuum since the substrate is damaged.
Meanwhile, the NEG uses titanium (Ti), Zirconium (Zr), or the like, as a main component and formed by adding other metals such as aluminum (Al), nickel (Ni), Cobalt (Co) or ferrite (Fe) and oxide.
The NEG heightens the degree of vacuum by removing a residual gas in a light bulb or an FED and used in various application field such as extension of durability of a device.
In the activation process of the NEG, after compressed and sintered power particles are combined, when they are first exposed in the air, a thin film of an oxide, a carbide and a nitride formed at the surface of the powder particles is removed.
In the activation process of the NEG, the material such as the oxide, the carbide and the nitride is heated to diffuse oxygen, carbon and nitrogen into the getter material, and then, the surface of the metal of the pure NEG, being in the activated state available for a gas adsorption, is exposed.
An activation temperature of the NEG depends on a composition. For example, a ST-707 produced and sold by SAES Getters of Italy is formed by activating an alloy of 70 weight % Zr, 24.6 weight % V and 5.4 weight % Fe at a temperature of 350xc2x0 C., and a st-101 is formed by activating an alloy of 84 weight % Zr and 26 weight % Al at a temperature of 900xc2x0 C.
The activation process is preferably performed at a low temperature for a short time in consideration of a damage to a function of a specific device, an energy and a processing cost, and these matters are much required for the thin film type display such as the FED using the glass substrate.
A technique related to the activation process that can be performed at a low temperature is disclosed in a Japanese patent publication No. xe2x80x988-196899xe2x80x99 and an International Patent Number xe2x80x98PCT/IT 97/00027xe2x80x99.
In the Japanese patent publication No.: 8-196899, an oxidation agent such as titanium (Ti), titanium oxide (TiO2) and a barium oxide (BaO2) is heated by a heater, mixed at a suitable ratio so that a reaction heat can be generated, and then pressurized in order to construct an NEG system of a certain shape.
As for the two oxides (TiO2, BaO2), in order to form Ti2O5, the intermediate oxide of titanium, titanium is partially oxidized.
The reaction heat according to the oxidation reaction should activate residual titanium, and the mixture is activated at a temperature of 300xcx9c400xc2x0 C.
The International Patent Number xe2x80x98PCT/IT 97/00027xe2x80x99 discloses a composition of a getter comprising oxide selected from the group of Ag2O, CuO and Co3O4 or their mixture and an alloy.
A third component such as yttrium and lanthanum existing in rare earth elements can be selectively added to the alloy.
In general, among the composition, the getter material requires a high temperature of 350xcx9c900xc2x0 C. for its activation, while the getter device containing all of the compositions can be operated at a temperature of 280xcx9c500xc2x0 C., a comparatively low temperature.
That is, the getter device can be activated at a comparatively low temperature by using a reaction heat using thermodynamic interaction with other element.
However, when the NEG alloy suddenly comes in contact with a large amount of reactive gas, that is, when it is exposed in the air, and when the initial alloy has a melting point of above 200xcx9c250xc2x0 C., the alloy makes a strong exothermic reaction to increase the temperature up to above 1000xc2x0 C.
Thus, there is a possibility that other portion of the FED panel is damaged, so that it can hardly be adoptable to the thin film display such as the FED or the PDP (plasma display panel; PDP).
Therefore, an object of the present invention is to provide a composition of is a getter and a field emission display (FED) using the same that are capable of improving a degree of vacuum and a gas rejection capability by performing an activation process by using a getter that can lower an activation temperature.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a composition of a getter of which a main component is Cr. The composition of a getter further comprises titanium (Ti) and Zirconium (Zr). The composition of a getter consists of 40 weight % chrome (Cr), 30 weight % titanium (Ti) and 30 weight % zirconium (Zr).
To achieve the above object, there is also provided a field emission display including a getter having chrome as a main component.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.